utsname.c

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/*
 *  Copyright (C) 2004 IBM Corporation
 *
 *  Author: Serge Hallyn <serue@us.ibm.com>
 *
 *  This program is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License as
 *  published by the Free Software Foundation, version 2 of the
 *  License.
 */

#include <linux/export.h>
#include <linux/uts.h>
#include <linux/utsname.h>
#include <linux/err.h>
#include <linux/slab.h>
#include <linux/user_namespace.h>
#include <linux/proc_fs.h>

static struct uts_namespace *create_uts_ns(void)
{
    struct uts_namespace *uts_ns;

    uts_ns = kmalloc(sizeof(struct uts_namespace), GFP_KERNEL);
    if (uts_ns)
        kref_init(&uts_ns->kref);
    return uts_ns;
}

/*
 * Clone a new ns copying an original utsname, setting refcount to 1
 * @old_ns: namespace to clone
 * Return NULL on error (failure to kmalloc), new ns otherwise
 */
static struct uts_namespace *clone_uts_ns(struct task_struct *tsk,
                      struct uts_namespace *old_ns)
{
    struct uts_namespace *ns;

    ns = create_uts_ns();
    if (!ns)
        return ERR_PTR(-ENOMEM);

    down_read(&uts_sem);
    memcpy(&ns->name, &old_ns->name, sizeof(ns->name));
    ns->user_ns = get_user_ns(task_cred_xxx(tsk, user_ns));
    up_read(&uts_sem);
    return ns;
}

/*
 * Copy task tsk's utsname namespace, or clone it if flags
 * specifies CLONE_NEWUTS.  In latter case, changes to the
 * utsname of this process won't be seen by parent, and vice
 * versa.
 */
struct uts_namespace *copy_utsname(unsigned long flags,
                   struct task_struct *tsk)
{
    struct uts_namespace *old_ns = tsk->nsproxy->uts_ns;
    struct uts_namespace *new_ns;

    BUG_ON(!old_ns);
    get_uts_ns(old_ns);

    if (!(flags & CLONE_NEWUTS))
        return old_ns;

    new_ns = clone_uts_ns(tsk, old_ns);

    put_uts_ns(old_ns);
    return new_ns;
}

void free_uts_ns(struct kref *kref)
{
    struct uts_namespace *ns;

    ns = container_of(kref, struct uts_namespace, kref);
    put_user_ns(ns->user_ns);
    kfree(ns);
}

static void *utsns_get(struct task_struct *task)
{
    struct uts_namespace *ns = NULL;
    struct nsproxy *nsproxy;

    rcu_read_lock();
    nsproxy = task_nsproxy(task);
    if (nsproxy) {
        ns = nsproxy->uts_ns;
        get_uts_ns(ns);
    }
    rcu_read_unlock();

    return ns;
}

static void utsns_put(void *ns)
{
    put_uts_ns(ns);
}

static int utsns_install(struct nsproxy *nsproxy, void *ns)
{
    get_uts_ns(ns);
    put_uts_ns(nsproxy->uts_ns);
    nsproxy->uts_ns = ns;
    return 0;
}

const struct proc_ns_operations utsns_operations = {
    .name       = "uts",
    .type       = CLONE_NEWUTS,
    .get        = utsns_get,
    .put        = utsns_put,
    .install    = utsns_install,
};